splitLogFileByDate.php

<?php

$handle = fopen($argv[1], 'r');
$handle || exit('no readable file');

$handles = array();

while (($line = fgets($handle)) !== false)
{
    if (preg_match('/^201.-..-../', $line, $match))
    {
        $date = str_replace('-', '', $match[0]);
        empty($handles[$date]) && $handles[$date] = fopen($argv[1] . '-' . $date, 'a');
    }
    fwrite($handles[$date], $line);
}

https://gist.github.com/hyperair/8b82650199622248d8ce